Digitizers, such as digital-to-analog converters (DACs) and analog-to-digital converters (ADCs), are indispensable elements in many systems, such as optical communication systems, wireless communication systems, satellite communication systems, computer data storage systems, image processing systems, video processing systems, sound processing systems, and controls systems, among others. The ability to generate and/or represent waveforms that closely adhere to waveforms as defined by system designers is of prime importance in many engineering areas. For example, accurate acquisition of waveforms and their digitization is a key component of contemporary signal processing systems.
Digitizers serve the purpose of converting information between the analog and digital domains. Analog-to-Digital Converters (ADC) capture analog physical quantities (current or voltages) by periodically measuring discrete samples, quantizing their amplitude into discrete values, and encoding them into their equivalent digital representations or values. Conversely, Digital-to-Analog Converters (DAC) generate analog signals from digital values by creating physical impulses (e.g., current or voltages) with amplitudes that correspond to the digital values. In this manner, for example, an analog signal or waveform can be converted into an equivalent digital signal or waveform, and vice versa.
Multichannel DACs and ADCs are typically used in communication systems that encode information in the electric field of electromagnetic waves. Two-channel DACs are often used to generate an analog representation of the real and imaginary (i.e., in-phase and quadrature) components of the full electric field; whereas, two-channel ADCs are often used to capture the digital representation of the real and imaginary (i.e., in-phase and quadrature components) of the full electric field. For example, four-channel digitizers (e.g., DACs/ADCs) are used in an optical communication system to generate and capture the real and imaginary components (sometimes referred to as in-phase and quadrature components) for each of two polarizations of the full electric field.
Each channel of some multichannel DACs includes a DAC for each respective channel, where each channel's respective DAC includes a respective digital input and a respective analog output. Likewise, each channel of some multichannel ADCs includes an ADC for each respective channel, where each channel's respective ADC includes a respective analog input and a respective digital output.
Unfortunately, inaccuracies created during the process of digitization negatively impact system performance. Some methods for improving the response of multichannel DACs and multichannel ADCs apply equalization methods to the digitizer ports independently. However, the attainable level of improvement in performance accuracy remains limited by crosstalk between those ports. Crosstalk between digitizer ports is often present due to the tight packaging used between individual digitizer devices in very large scale integration (VLSI) technology, which causes digitizer signals to leak to adjacent ports during signal digitization.
Some methods attempt to improve digitization accuracy/fidelity of the digitizers by separately digitally filtering each of the DAC or ADC ports, but these solutions generally have a residual error in attainable fidelity. Other methods attempt to improve digitization accuracy using look-up-tables, but these methods still are unable to circumvent the effects of crosstalk between the ports. Thus, the digitizers fall short from their expected accuracy.